Current regulator



Feb. 26, 1963V R. o. MGCARY CURRENT REGULATOR Filed May 3l, 1960 Illlk United States Patent 3,079,541 CURRENT REGULATOR Richard 0. McCary, Phoenix, Ariz., assigner to General Electric Qompany, a corporation oi New York Filed May 3i, 1960, Ser. No. 32,887 6 Claims. (Cl. 323-7) This invention relates to a system for the regulation of current supplies and more particularly to a system for providing driving currents of accurately regulated magnitudes for magnetic core memories.

In the design of magnetic core memories employed in digital computer systems, it is necessary to provide driving currents of accurately regulated magnitudes. Although this invention is directly concerned with that problem, it should be understood that it is useful wherever it is necessary or desirable to provide one or more accurately regulated sources of current of different magnitudes.

In order to provide selectively timed drive-current pulses of a given magnitude to drive windings of a magnetic core memory system, it has been customary to employ a selectively operable switch to connect a resistor having large resistance, as compared to the load impedance of the drive windings, to an appropriate voltage source. Since the load is a magnetic core memory drive winding, its apparent reactive impedance varies depending upon the information stored in the cores being driven. Therefore, when the switch is selectively operated, and the voltage source is thereby connected to the drive windings through the resistor in order to provide a pulse of current which will switch all of the cores being driven to a common stable state, the rise of current through the drive windings is exponential and the rise time varies depending on the information stored in the cores.

It is usually considered desirable or necessary to have either a linear rise of current or a very short and constant rise time. To accomplish that, a large voltage source and a large resistor are employed with the result that the power dissipated in the resistor may be inordinate and if the switch is to be a transistor, the voltage employed may exceed the capabilities of the switch.

Various techniques may be employed to reduce the potential of the voltage source and to reduce the power dissipated. One technique consists of placing an inductor in series with the resistor. The resistor is selected to have the resistance necessary to establish the magnitude of the current and be approximately equal to the apparent core line resistance. The inductor is selected to be very large. Variations and refinements of this technique for providing a timed current pulse of a given magnitude to magnetic core drive windings have been devised. However, some provide unsatisfactory current regulation and others are either too complex or expensive, or both, for general applications in digital computer systems.

The object of this invention is to provide a system for accurate regulation of current to a load having small power losses.

Another object is to provide a plurality of regulated current sources, each having a small power loss and each being isolated with respect to the others so that it may be adjusted to be at any desired magnitude.

More particularly, the object of this invention is to provide driving current pulses of accurately regulated magnitudesto drive windings of a magnetic core memory with a minimum of power losses.

These and other objects of the invention are achieved in a system wherein a plurality of current transformers are provided, the primary winding of each being connected in series with the primary windings of the others. The secondary winding of each transformer may be provided with several taps so that different current magnitudes may be selected. In that manner it is not only possible to provide sources of current at different magnitudes but it is also possible to isolate the circuit of each from all other circuits except its associated load circuit. A current regulator consisting of a series-connected saturable reactor provides a constant alternating current to the primary windings of all of the current transformers which are connected in series. This current is regulated by applying negative feedback for one of the current sources through a feedback amplifier comprising a magnetic amplifier. Since each current source includes a rectifier and filter, the signal from a current source applied to a control winding of the amplifier is a substantially constant direct current. Because the output of the amplier is also rectified and tiltered, a substantially constant direct current is applied to a control winding of the current regulator. The rectified and filtered output currents of the remaining current sources are applied to respective dummy load resistors through a switch, each dummy load resistor being selected to have a resistance substantially equal to the apparent resistance of an associated core winding or load to which the associated current source may be connected by operating the appropriate switch.

The sole gure schematically illustrates an embodiment of this invention. It should be understood that the invention is in a system for providing regulated current sources and not in illustrated component parts such as the series-connected saturable reactor, the magnetic ampliiier, or the individual current sources, as such.

The series-connected saturable reactor ot the current regulator consists of a pair of magnetic cores it? and 11 having respective windings 12 and 13 connected in series. Each core is of material suitable for cores of magnetic ampliiers and the windings are helically wound around the cores in such a manner that the sense of the winding of each is as indicated by the convention of placing a dot at one end. Additional windings 14 and i5 are wound around both of the cores l@ and lll in a manner such that the sense of each relative to the windings l2 and 13 is as indicated by a dot placed at one end of each. The winding i4 is employed to provide a bias current to the saturable reactor from a source of +50 volts D.C. through a resistor 16 and a iilter consisting of a capacitor 17 and an inductor 18. The winding 15 which receives a substantially constant direct current through an inductor 19 is employed to control the series impedance presented to alternating current through the windings i2 and 13. The net ampere-turns of the windings i4 and 15 establish the operating point of the series-connected saturable reactor.

The current regulator should have inherently fast response for line and load transients in addition to very high etiective internal impedance. Accordingly, a high control circuit impedance is desired. The inductor i9 is selected to have large inductance in order to provide a high control circuit impedance. Such a large inductance causes variations in the control current to be very slow. However, the control current will not have rapid changes due to line or load transients in the system of this invention so that there is no real disadvantage in having slow response to variations in the control current.

The series-connected saturable reactor employed in this invention as a current regulator will not be further described since its theory and operation has been adequately described in literature such as in Chapter Eight of Magnetic Amplifiers by Dr. Herbert F. Storm, published by John Wiley 8c Sons, Inc. (1955). In order to fully understand this invention, it is suicient to appreciate that the alternating current through the primary windings of transformers 21, 22 and 23 is a 400 cycles per second alternating current having a substantially square waveform. The frequency of the alternating current is not important and has been selected in the illustrated embodiment of this invention for convenience only. The

tional to the control current through the winding since the saturable reactor is connected as a series impedance with the transformers 2l, 22 and 23 such that as the c011- trol current is decreased, the apparent reactive vimpedance of the Vwindings l2 and 13 increases and causes a decrease in the ampliude of the alternating current through the transformers.

The output current from the secondary winding of the transformer 2i is rectified by a bridge rectier 2S and filtered by a capacitor 27 andan inductor 23 to provide a direct current to the feedback amplifier. The current output from the secondary winding of the transformer 22 is similarly rectilied by a bridge rectifier 35 and ltered by a capacitor 37 and an inductor 38 to provide substantially constant direct current through a dummy load resistor 39 via a switch 4t?. A load 4l consisting of drive windings of a magnetic core memory is connected between a sec-Y ond contact of the switch di) and the junction between the capacitor S7 and the resistor 39 so that when the switch 40 is moved to its alternate position it makes contact between the inductor 38 and the load 4i. Diodes 42 and 43 maybe provided to control the current rise time through the load in order to protect the switch when necessary, such as when the switch includes a transistor.

Additional loads consisting of drive windings of the magnetic core memory, such` as a load 44, may be connected to additional current sources, such as the current source consisting of the transformer 25, a bridge rectier 45, a capacitor 47, an inductor 48, a dummy load resistor 49 and a switch 50.

It should be noted that the current magnitude for each load may be individually adjusted to a predeterminedlevel by selecting an appropriate tap on a secondary winding of the transformer to which it is associated. Also, it may be seen that the reason any given current source may be set at any magnitude is that each current source is isolated from all other circuits except its load. It should further be noted that the primary windings `of current transformers in any number of these current sources may be connected together in series with the current regulator which provides the same regulated alternating current through all of the transformers. Regulation is obtained in a novel manner by a feedback loop through the magnetic amplifier', as will be presently described.

The magnetic amplifier consists of a parallelconnected saturable reactor with blocked intrinsic feedback including a pair of magnetic cores 60 and 61 having respective windings 62 and 63 oppositely wound and connected in separate yparallel circuits. One parallel circuit consists of one half of the secondary winding of a center tapped transformer 64 and a rectifying diode 65 and the other consists of the second half of the secondaryof the transformer 64 and a rectitying diodeY 66. Since the windings 62 and 63 are in parallel circuitsand the diodes 65 and 66 provide rectification, current from a 120 volt A.C. power source coupled bythe transformer 64 to the windings 62 and 63 is full-wave rectied and then filtered by a capacitor 67 to provide direct current to the control winding 1 5 of the current regulator.

The power source applied to the primary winding of the transformer ed has been selected for the illustrated embodiment of this invention for convenience only Vand it should be understood that the power source provided for the amplifier may be completely independent of the power source providedk for the current regulator as to both amplitude rand frequency.

The magnetic amplit'ier includes a control winding '7d whichis wound about both cores 60r and 6l in a direction indicated by the dot placed adjacent to it. A bias winding Il and a temperature compensating winding 72r are also wound around both of the cores 6d and nl, the winding direction of each being the same as that of the -control winding as indicated by a dot placed at one end of each.v The bias winding is provided with a direct current from a regulated source 73 which includes three potential regulating Zener diodes 74, 7S and '76 connected in series between a source of -50 volts D.C. and `8 volts D.C. A resistor '77 is connected in series with the control winding 7d in order to adjust the load of the feedback current source to be substantially equal to the loads of the other current sources.

The parallel-connected saturable reactor with blocked intrinsic feedback employed as an amplifier inthe feedback loop is in effect an impedance connected in series between the transformer 64 and the control winding 15 of: the current regulator. When the cores dit and 6l saturate,rtheir apparent reactive impedance is low 'and alternating current through the coils 62 and d3 is high. rl`he design of the reactor is such that, with zero current in the windings 7d, 7l and 72, it is self-saturating; that is, the core saturates very quickly at the beginning of each power supply half cycle and then high current flows making maximum full-wave rectified current available to the control winding l5 of the current regulator. The degree of saturation determines the effective impedance in series with the control winding l5 of the current regu- Y lator and can be established by an adjustment of a resistor 78 which controls the magnitude of current through the ybias winding 7l which ows in such a direction as to enhance the self-saturating 'current or" the reactor. The magnitude of the feedback current through the control winding 7@ is then adjusted to pro-vide sufficient current and in such a direction as to oppose the self-saturating current of the reactor. The net ampere-turns of the windings 7d and 7l establish the operating point of the reactor, disregarding for the present current throughV the winding 72 which adds to the feedback ampere-turns and which is normally constant.

ln operation, the current magnitude provided by the current sources is established by adjustments of the resistors 78 and le. If the current magnitude varies for reasons associated with the power source or the loads, the current through the control winding 70 changes proportionately thereby altering the degree of saturation Yof the cores 6d and 61,. Thus, if the current through the control winding 79 decreases, the current through the control winding l5 of the current regulator increases, thereby increasing the degree of saturation of the cores l0 and ll, decreasing the apparent reactive impedance ofthe windings l2 and 13 and increasing the current to the primary windings of the transformers 2l, 22 and 23, Conversely, if the current supplied lby the sources increases, the curent to the control winding 15 decreases and the current to the primary windings of the'transformers 2l, 22 and 23 decreases, thereby decreasing the current provided by the current sources. Y

The parallel-connected saturable reactor with blocked K intrinsic feedback employed in this invention as la feedback amplifier will not be further described since its theory and operation has/been adequately described in literature such as in Chapters 15 and 20 of the aforementioned book by Dr. Herbert F. Storm.

If the loads connected to the power sources, such as the loads 41 and 42, are magnetic core drive windings as in the illustrated embodiment of the invention, it is frequently necessary or desirable to provide some ternperatnre compensation for the drive current supplied to. the cores. Accordingly, a thermistor @il is placedrin they environment of the'drive windings so that as ytemperature increases, its impedance decreases andcurrent to the temperature compensating winding 72 increases.

terminal of the temperature compensating winding 72 is connected to the point of reference potential.

As the current through the temperature compensating winding increases, the ydegree of saturation of .the cores 60 and 61 decreases to provide a decrease of current flow through the control Winding 1S thereby decreasing the amplitude of the current sources supplying the loads 41 and 42 in the magnetic core memory and providing more stable operation of the magnetic core matrix over a Wider range of ambient temperature. If a temperature compensating Winding is not employed in the magnetic ampliiier of the present system for providing regulated drive currents for a magnetic core memory, it may be necessary to take other measures for assuring adequately stable operation such as regulating the environmental temperature of .the magnetic core stack of the memory.

While the principles of the invention have now been made clear in an illustrative embodiment, there will be immediately obvious to those skilled in the art many modiiications in structure, arrangement, proportions, the elements, materials, and components, used in the practice of the invention, and otherwise, which are particularly adapted for specific environments and operating requirements, without departing from those principles. The appended claims are therefore intended to cover and embrace any such modifications, Within the limits only of the true spirit and scope of the invention.

What is claimed is:

l. In a system for the regulation of current to a load, the combination comprising: a current transformer having a primary winding and a secondary winding; a variable impedance means connected in series with said primary winding of said transformer, said impedance means comprising a saturable reactor having a control winding; means for coupling said current transformer and said variable impedance means in series with a source of alternating current and said load; and a negative feedback means coupling said secondary Winding of said transformer to said control winding, said negative feedback means including a current amplifying means, a source of constant biasing current coupled to said current amplifying means, a current rectifying means coupling said current amplifying means lto said secondary Winding of said current transformer and means for coupling said amplifying means to said control winding of said saturable reactor.

2. A system for the regulation of a current supply comprising: a current transformer having a primary winding and a secondary Winding; a series-connected saturable reactor having a control Winding; a parallelconnected saturable reactor With blocked intrinsic feedback having a control Winding and a reference Winding; means for connecting said series connected saturable reactor in series with said primary Winding of said current transformer, a load and a source of alternating current; means for coupling sa-id parallel-conectad saturable reactor in series with said control Winding of said seriesconnected saturable reactor and a source of current; means for connecting said reference winding of said parallel-connected saturable reactor to a source of constant direct current; and rectifying means for connect-ing said secondary Winding of said current transformer to said control winding of said parallel-connected saturable reactor.

3. In a system for providing a plurality of sources of currents having accurately regulated magnitudes, the combination comprising: a plurality of current transformers each having a primary winding and a secondary Winding, a series-connected saturable reactor having a control Winding; a parallel-connected saturable reactor with blocked intrinsic feedback having a control winding and a reference Winding; means for connecting the primary windings of said current transformers in series with said series-connected saturable reactor and a source of alternat-ing current; means for coupling said parallel-connected saturable reactor in series with a source of alternating current and said control Winding of said seriesconnected saturable reactor; means for connecting said reference -winding of said parallel-connected saturable reactor to a source of constant direct current; rectifying means for connecting a secondary winding of one of said current transformers to said control winding of said parallel-connected saturable reactor; and means for coupling the secondary windings of each of the other current transformers to different loads.

4. In a system for the regulation of currents to a plurality of independent loads, the combination comprising: a plurality of current transformers, each having a primary winding and a secondary winding; a variable impedance means; means for connecting said variable impedance means and primary windings of said current transformers in series with a source of alternating current; feedback means coupling a secondary Winding of one of said current transformers to said variable impedance means for decreasing its impedance when current induced in said secondary Winding decreases and for increasing its impedance when current induced in said secondary Winding increases, whereby current induced in said secondary Winding is maintained constant; and means coupling the secondary Winding of each of the other of said current transformers to an independent load.

5. In a system for the regulation of current to a load the combination comprising: a current transformer having a primary Winding and a secondary Winding; a var-iable impedance means connected in series With said primary winding, said variable impedance means comprising a saturable reactor having a control winding; means for coupling said primary Winding and said variable impedance means in series with a source of alternating current and said load; and a negative feedback means coupling said secondary Winding of said transformer to said control Winding, said negative feedback means including `a current rectifier and a magnetic amplifier comprising a parallel-connected saturable reactor having blocked intrinsic feedback, a reference Winding adapted to be connected to a source of constant direct current and a control winding coupled to said secondary winding of said current transformer by said rectilier, said parallel-connected saturable reactor being coupled in series with said control Winding of said variable impedance means by a rectifying means.

6. In a system for the regulation of current to a load, the combination comprising: a current transformer having a primary Winding and a secondary Winding; a variable impedance means, said impedance means comprising a series-connected saturable reactor having a control Winding; a source of alterna-ting current; means for coupling the primary Winding of said current transformer in series with said variable impedance means, said load and said source of alternating current; a negative feedback means coupling the secondary winding of said current transformer to the control winding of said seriesconnected saturable reactor, said feedback means comprising a parallel-connected saturable reactor having a control Winding, a first coupling means for coupling the secondary Winding of said current transformer to the control winding of said parallel-connected saturable reactor, said iirst coupling means including a first current rectifying means, a second coupling means for coupling said parallel-connected saturable reactor in series with said current source and the control Winding of said seriesconnected saturable reactor, said second coupling means including a second current rectifying means.

References Cited in the le of this patent UNlTED STATES PATENTS 2,633,562 Rocard Mar. 3l, 1953 

1. IN A SYSTEM FOR THE REGULATION OF CURRENT TO A LOAD, THE COMBINATION COMPRISING: A CURRENT TRANSFORMER HAVING A PRIMARY WINDING AND A SECONDARY WINDING; A VARIABLE IMPEDANCE MEANS CONNECTED IN SERIES WITH SAID PRIMARY WINDING OF SAID TRANSFORMER, SAID IMPEDANCE MEANS COMPRISING A SATURABLE REACTOR HAVING A CONTROL WINDING; MEANS FOR COUPLING SAID CURRENT TRANSFORMER AND SAID VARIABLE IMPEDANCE MEANS IN SERIES WITH A SOURCE OF ALTERNATING CURRENT AND SAID LOAD; AND A NEGATIVE FEEDBACK MEANS COUPLING SAID SECONDARY WINDING OF SAID 